ABSTRACT People have kept companion animals for millennia, a tradition that implies mutual benefits due to its persistence; however, scientific investigations present mixed results. Some research suggests pet owners are less lonely than non-owners, but other findings suggest pet owners have higher psychological distress. Research comparing owners with non-owners is limited, and methodological inconsistencies need to be addressed. This study investigated social support and wellbeing (positive functioning) in cat and dog owners, informed by social support theory, attachment, and social exchange theories. It was hypothesized that (1) pet support would predict wellbeing in addition to human support and (2) at least one aspect of pet–owner relationship quality would influence the relationship between social support and wellbeing. An adult sample of 89 cat owners and 149 dog owners (n = 238; 205 females and 33 males) completed an online survey comprising a demographics questionnaire, the Multidimensional Scale of Perceived Social Support, the Cat/Dog–Owner Relationship Quality Scale, the Psychological Wellbeing Scale, and Satisfaction with Life Scale. Social support measures included some demographics on theoretical grounds to measure the construct multidimensionally. Hierarchical and multiple regressions were conducted, and results indicated that both hypotheses were supported: having more pets significantly predicted greater psychological wellbeing in addition to human social support. Unexpectedly, perceived pet support significantly, positively predicted life satisfaction when perceived emotional closeness with pet was low. These findings indicate that pets may improve psychological functioning and that emotional closeness is an important moderating factor. Practical implications include the social benefits of pets for those who could benefit from greater psychological functioning and improved life satisfaction.